EX-7601 osc: walk chunk unaligned RPC correctly

EX-7601 osc: walk chunk unaligned RPC correctly

For decompression, the client must start looking for
compressed chunks at a chunk aligned offset.

Implement this in decompress_request.

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I3273135990ddf51e8b3c651734e19350e91f659c
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/52933
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Artem Blagodarenko <ablagodarenko@ddn.com>